This invention relates to a process for preparing a rigid polyurethane foam, and a laminate article containing such foam, from a urethane-modified polyisocyanate.
Rigid polyurethane foam is extensively used in the appliance and construction industry where its attractive thermal insulation performance is valued. Unfortunately as such rigid polyurethane foam frequently can be friable it is often necessary to protect it from physical damage by use of a protective facing material. The selection of suitable facing material is generally application related and can be for appliance units, a plastic; for rigid insulation boardstock, paper; or for refrigerated containers or roadstock, metal. End products comprising a facing material and rigid polyurethane foam desirably should exhibit an overall attractive structural strength and durability. To help provide for such traits, the foam advantageously should exhibit attractive adhesion properties to the facing material and not be particularly susceptible to internal failure, for example tearing.
The adhesion of foam to a facing material can be enhanced by pretreatment of the facing material using generally known methods including corona treatment. Alternatively, enhanced adhesion properties may be obtained by selection of the materials used to prepare the polyurethane foam. Patent publication EP-A-462,438 discloses the use of certain urethane-modified polyisocyanates when preparing water-blown rigid polyurethane foam exhibiting improved adhesion properties to a solid surface, notably metal. Further improvement of the disclosed adhesion properties would be desirable to better meet the demanding industrial performance requirements. Additionally, it would be desirable to develop a foaming process wherein an article comprising a facing material and a rigid polyurethane foam can be prepared under more convenient processing conditions including, for example, a lower process temperature without substantial loss of adhesion properties.